This invention relates to recording devices, particularly the type in which several fixed recording members are arranged along a row transverse to the transport direction of a record carrier for continuously recording variations in values as line diagrams along several tracks.
In contrast to recording arrangements in which a single writing instrument is moved in proportion to the quantity measured, each recording element of such recording arrangements traces a line or bar along a recording track reserved for a predetermined value range as long as the value detected is within this predetermined range. Such step-like recorders should provide conspicuous and easily readable indications which are also inexpensively machine readable. For this purpose, the values being sensed and recorded must be quantizable, and the effects of the discontinuities in the indications should be overcome.
The above requirements are usually obtainable in so-called self-deleting recording devices where the rate of change of the quantity measured is small compared to the speed of the record carrier. These kinds of recording devices stress only variations of measurements just prior to a particular event while earlier indications are ignored. This emphasis permits the recordings to be stretched out to achieve high resolution over a period of time. A typical example is a vehicle-mounted device called an accident recorder which particularly maintains a record of the speed of a vehicle over the distance most recently travelled. The aforementioned step bar graphing is particularly suitable for such a recorder because it allows one interpreting the record to attribute indication to specific speed ranges.
The desired recording apparatus with its fixed arrangement of several recording members in a row has a decided advantage from the technical point of view. It avoids rigid recording means which are moved relative to the record carrier, generally in dependence on the sensed values. This makes the recording device less sensitive to shocks, reduces its service expenses and also simplifies production and mounting. On the other hand, the usually restricted recording space available on such a record carrier cannot be optimized. This is so because the recording members, which are assembled as a recording comb, cannot be arranged as close to each other as desired due to space and production limitations.
Under the circumstances, display resolution of the quantity measured is limited, and in many cases unsatisfactory. Often, it is at least important to know whether the actual value measured is nearer the lower or upper limit of the range indicated. Therefore, proposals have been made to use a recording comb which is itself movable transverse to the recording direction of the record carrier. However, this has known disadvantages, such as the need for expensive mechanical parts and a movable current input, and has the effect of generating noise.